Chemical composition and process for aluminum etching



is orderta inhibit the scale formation;

CHEMICAL COMBBSITiUNrAND, PROCESS FOR ALUMINUM ETCHING John-T. Massengale, Ahingtong and Robert H.;El l iott,;Jr.,

Oreland; Pa., assigiiorjs to"Pennsalt Chemicals Corporation, a c'o'rpo'ration of Pennsylvania NoDrawing. Application Match 31, 195;

SeriaPNo. 499,502.

14Claimsi (Cl. 41 4*2)- This" invention relates to anti-scaling bmpdsitionslfiir use in alkaline etching batli's and totthe-utilization ofsuch anti-scaling compositions inthe etching of aluminum and v aluminum base alloys. The term etching as used herein, both in; the specification andxclai'rns, includes] notonly light surface etching, b'ut chem-i'ca'l dissolution of s ubstaii tia-l 'am'ountsa ofithe" metal treated as occurs when fo'rining metal objects through cont-rolled selective: chemical-dis solution; a piocess frequentl-y referred to as chem niill iii-g1 v t The Conventional industrial practicei'n etching alu' Ininuine and aluminum base alloys is to treat the" surface of. the article to be etched with a hot aqueous' 'soli1'tion containing: an etching alkali such as sodium hydroxide,

potassium hydroxide; sodium carbonate, tris'odium p'ho's phate and the like, oi with mixtures" ofth'esematerials. The aluminum reacts with the alkaline etching materials; and where sodiumhydroxideis used asthe" etclia'nt; a solution'ofi sodiurn aluminate is formed. Ho'wevem wlien the: concentration; of alkaliiin theetchingbath is reduced below a certain value; the sodiumaluminate in-Ithe liftion reacts with waterand'thehd result ofthis react is'ther formation ef a' hard scale which is depb's'ite'd on the sides and-bottom of the tank containing the etolian't and: onheating coilsor other equipment which may 6e submergedwithinthe tank. This scalei's primarily ailiifmina, having the formula Al O .3H O:-

1 It has' generally been believed that airlines are unsuitable as additives% to aluminum e'tch-in'g baths for the prevention or inhibition ofi seale formation. Hbvvever, i-n= 'co pending application Sert- Not- 474 ;O36,' a'= formula: tion is 'd'escribed in whiehethylene diaminetetra acetie acid is used in conjunction with tartaric acidan'd'pre-f' erably inconjunction with tartaric acid; glucose" and cei' tain metal ions to prevent scale formation.

Though ethylene diamine tetra-aceticacid is effective for scale'inhibition when used together with tartaric acid, glucose and certai'rimetal salts irrthe' roportion-Siam manner described in" co-pe'ndin'g applicatioli s'e'r No. 47-4,- 036, the ethylene diamine-tetr-a at'ze'tie acid is in tfe ive when used alone and'iii some instances a'c'mauy promotes scale formation.

It has 110W been discovered tlia t c'eita have excellent scaleinhibiting prop sf when ad ed to causticaluminum et'chfiii'g'- solutions.- Furthermore, these "inifiesareefie'ctivei andoftlims'dves; itno't being neeessary to formulate 'th' with other materials yar'bsy'amines w 2,872,301 Patented Feb. 3, T959 TABLE I Goncentratioudf Additive Additive 3" v .4 5 1.0 gram gra gram gram Crude glucan tne S T N Crude glucamlne made in accord- ,ance-wlthg eferred'condition '1? N N, t Mpnoglucam e 4 S T N Diglucaminen T N' N N t N. N: S S S S S S, S S S m (The data' for this' table was obtained as follows: Sepe e solutions were prepared containing 30 grams caustic soda, 600 ml. water and' scale inhibitor in the amount iiidicatediii the table's. These solutions were then heated to 15Q F. at which temperature 18.5 grams ofialuriiinurn metal were dissolved in each solution. The solutionsv'vere then permitted towel and stand for 18 1i is after' which time they were observed for scale formation.)

It will be noted from the difier'en't types of hydroxy amines of TableI that the least efiective,in preventing scale formation, are the normal alkyl hydroxy. amines where R or R' of the above general formula is a normal a'lk'ylf g'rou'p'; Why these amines are not as effective as thdoth'er hydroxy' amines of this general type is not understood. However, they do have an appreciable-effect in} reducing or preventing scale formation and may be used where the etching bath is not subjected to severe operating Conditions; 7

Y The droiiy amines of'Table I all have in common th ey arerepare directly from monosaccharides by reductiveamination (i'. e; by reaction of inonosaccharide with ammonia or an alkyl substituted ammonia and hydrogen under the" influence of a hydrogenating catalyst siich as nickel) or are products subsequently formed by reacting the initial products of the reductive amination with oi oi Q halo fatty acids'to form N-oc or N[-1 carboiiyifiethyl'alkyl" derivatives These amines which consftit'ute a class" formed by the reductive a'mination of Glutamic i TABLE II Concentration of T Additive Additive 1 gram 3 grams Aspartic acid Ethylenerliaminn Ethylenediamine tetraacetic acid Hexamethylenetetramine fluosillcate Glucosamine Triethylaminm Glucose. Monoethanolamine Tripthnnnlnminp mmmmmmmmmmm mmmmmmmmmmm (The data for Table II was obtained in the same manner as that for Table I, the conditions being the same, with the exception of the additive used.)

Though any of the reducing sugars may be employed in preparing the sugar amines for scale inhibition glucose ing mol ratios of ammonia to glucose of about 1.5 :1 to

is generally P eferred because of its ready availability and '1 low cost.

Of the glucamines, diglucamine is the most efiective in preventing scale formation, it being preferred to the monoglucamine. In its preparation, however, a substantial amount of the monoglucamine is formed so that the crude Y product contains essentially a mixture of both the mono and diglucamine. It has been found that'when the amination is carried out under certain conditions, the scale inhibiting properties of the crude is, in many instances, better than that of the monoglucamine and-equal to that of the diglucamine which is excellent.

It the crude is prepared with a water content of about 10 to 15% by weight, the product is readily mobile at temperatures of about 50 C. and can readily be sprayed onto the caustic or other solid alkali while blending in preparing the final aluminum etchant composition. Furthermore, the physical properties of the crude are such that they prevent any dustiness in the final blend. This is of considerable advantage, since caustic formulations are frequently quite dusty, the dust causing irritation and frequently requiring the wearing, by workers,'of protective garments and masks.

The crude glucamine compositions which are most effective in scale inhibition, are prepared in the following manner:

Glucose and ammonia, generally as aqueous ammonia, are added to a pressure reactor along with a hydrogenation catalyst such as nickel. Hydrogen is then introduced under pressure and the reactants heated, with agitation, at a temperature preferably below 75 C. until hydrogen uptake is substantially complete. If some caustic has been added to the reactor, hydrogen uptake will begin at about 5254 C. However, without the caustic present, hydrogen absorption does not begin until about 67-70 C.

Towards the end of the reaction, the temperature is increased to complete hydrogen takeup. However, the temperature should preferably not exceed 100 C. since side reaction products tend to form at the higher temperatures which apparently adversely affect the scale inhibiting properties of the crude. Glucamine crudes having excellent scale inhibiting properties are obtained by employ- 62:1. The preferred ratio is in the order of about 2.2 mol of ammonia to 1 mol glucose.

Though the ratio of ammonia to crude does not seem to greatly affect the scale inhibiting properties of the resulting product, particularly within the above limits, the hydrogenation pressure, i. e. the pressure at which the hydrogen uptake occurs, appears to have a substantial effect. Thus, crudes prepared at pressures of about 250 pounds per square inch gage are not particularly satisfactory unless an exceptionally large amount of hydrogenation catalyst is used. This is well illustrated in the fol lowing table:

TABLE III Ni Results Gram Mols NHz/glucose Catalyst, Pressure wet basis Mild Severe test test 125 1,000 good 800-520 good.- good. 815 25 125 125 125 72 500 good...- fair (In the above table, the nickel catalyst is given on a wet weight basis; on a dry basis the weight is about half the amount given. The data for Table III was obtained by using caustic solutions containing 30 grams caustic soda, 600 ml. water and .5 gram of crude glucamine. The aluminum was dissolved at a temperature of C. and the solutions observed after 18 hours standing. In the mild test only 18 grams were dissolved. While in the severe test 18.5 grams of aluminum was dissolved. After 18.5 grams of aluminum has been dissolved, substantially all of the free caustic has been consumed and the solution is essentially incapable of dissolving more aluminum.)

After the hydrogen takeup is completed, the crude is removed from the reactor and filtered to remove the nickel catalyst. Suflicient water is then removed from the crude, preferably by heating under a vacuum, to give a product having a water content of about 10' to 15%.

Though the normal alkyl glucamines, such as normal ethyl glucamine and normal butyl glucamine, are not as effective scale inhibitors as either mono or diglucamine, the normal carboxy alkyl glucamines have excellent scale inhibiting properties.

For purposes of illustration, the following preparation of methyl carboxy glucamine is given:

Crude glucamine, in the amount of 210 grams, prepared as above described and representing 1 mol of nitrogen containing product, as shown by titrations (210 being the apparent molecular weight), was dissolved in 500 cc. of distilled water containing 106 grams (1 mol) sodium carbonate. To this was added 94.5 grams (1 mol) chloroacetic acid and the mixture refluxed for five hours.

This product was dried to a substantially anhydrous condition by evaporation of the water on a steam bath under vacuum. The product consisted primarily of methyl carboxy glucarnine.

The normal alkyl glucamines appearing in Table I were prepared in much the same manner asthe glucamines. The following description of the preparation of normal butyl glucamine will serve to illustrate the preparation of these materials. Butyl amine in an amount of 7.1 mols, and glucose in an amount of 3.2 mols were heated in a steam bath to a temperature of about 70 C. for 30 minutes, after which time a clear solution resulted. This solution, together with 3100 cc. of water and 188 grams of adrained Ranienickelzcatalyst (approximately. lofi grams actual nickel content) wereplacediin.a2gallon. stainless steel:autoclave.v of. the stirrer type. Hydrogenwas then introduced under a pressure of'1000 pounds. per square inchv gage. over a. period of 7 hours. while. the. reactants were maintained at a temperature of60. to.6'5 C. The reaction was. then.discontinued, the. reaction mixture. filtered" to remove the nickel catalyst and tl-ie'nl'eft' to stand over night at room temperature. The crystalliheprodilct which formed was filtered from the/mother liquor, washed and air dried. This product which melted" at 130.2 to 134 C. was normal bu'tylgliicamine. t

' In practicing, the invention,,the mono. and idigliicarnines and the carboxy alkyl glucamines are preferably used with the caustic in: amounts. of 1.5% to. 5 by weight based on the caustic soda. However, these materials will inhibit scale formation wh'enicoucentration's of as little as 0.5% areused and may be used in such lower concentrations where the caustic etchant solution will not have severe. working. However, for. general operation, as stated"; it is preferredto have these materials present in amounts of at least 1.5 There appears to be no detrimental efiect resulting from using these sugar amines in higher concentrations up to and above their saturation point.

The alkyl glucamines such as normal ethylglucamine, normal butyl glucamine etc., when used in concentrations of 3% tend to cause foaming. It is not clearly understood whether this foaming is a property of these alkyl glucamines or whether it is due to impurities present, such as decomposition products which may be formed in their preparation. However, where foaming is not a problem or where foam depressants are added to prevent or minimize the foaming, these alkyl glucamines may be employed at the concentrations indicated.

The etching of aluminum with compositions using these sugar amines as scale inhibitors is best illustrated by the following examples:

Example I A blend was prepared of a glucamine crude, prepared in the manner above described and caustic soda, containing 2.2% of the glucamine crude and 97.8 of flake caustic soda. The glucamine crude used had a syrup-like consistency and contained 12% water.

450 pounds of the blended composition was charged to a 600 gallon tank of water. Titration showed that the concentration, after charging was 4.2 ounces of compo sition per gallon of water.

This solution was then used for etching aluminum parts on a production basis, the parts being etched for about five minutes at 150 F. The etching operation was continued for eight hours a day for five days during which time solution additions were made to maintain the concentration between 2 and 5 ounces of the caustic per gallon. At the end of the fifth day the viscosity of the etching solution, due to the sodium aluminate held in solution, had increased to a point where it was difficult to rinse the etched parts. The specific gravity of the solution, at this point, was 1.18 at 90 F. Because of this high viscosity the tank was emptied. Inspection of the tank showed that no alumina scale had formed. At the bottom of the tank, prior to emptying, about two inches of soft sludge was observed. This sludge was found to be made up of the alloying elements, such as copper, manganese and zinc, which were present in the aluminum parts that had been etched.

Example II A caustic aluminum etching composition was prepared by blending glucamine syrup containing approximately 12% water and caustic soda to give a composition having 3% glucamine syrup and 97% caustic soda.

The resulting composition was added to 2500 gallons of warm water in the amount sufiicient to give a concentration of 5 ounces per gallon. This solution was used fonetching. aluminum. articles, the solution being. in use for two. days during. which time. some additions: were made to maintain the concentration at the 5 ounces per gallomlevel. I p 7 When the specific gravity; of. the etching solution had" reached 1.195 at "Fi thesolntio'n'was anm eannd uie tank carefully observed. No scale formation was noted;

During the etching process a foam blanket about two inches thick was formedon: the top ofi the etching solution. This blanket was particularly helpful in preventing caustic solution going into the air as fine spray, such spr'ay's ordinarily Being quite irritating to the workmen carrying ouraltiminum etchingoperations:

Thoughin-thespecific examplesg'iven; the sugar amines areemployed in so'lu'tiuns of etching alkali wherein the alkali is presentinamountswfabout '5' oun pergallon of'solutidn, they'iar'e' eifctive in'any'soluti siifiteiently alk'a'lin'e to etch-'thealuminum. E'tchin'g solinien's-as used are genera-lly-withinthe concentration range of '1 to" 1 5 by weight etching alkali.

. Having thus described our invention we claim:

1. The method of etching aluminum comprising treating said aluminum at an etching temperature with an aqueous solution of an etching alkali containing, in an amount sufficient to prevent scale formation, a hydroxy amine having the general empirical formula OHzOH(CHOH),,CH N

wherein n is at least 2; R is any of the group consisting of hydrogen, another CH OH(CHOH),,CH -radical, a normal alkyl radical containing not more than 4 carbon atoms, an oz carboxyalkyl group containing not more than 4 carbon atoms and a ,8 carboxyalkyl group containing not more than 4 carbon atoms exclusive of the carbon in the carboxy group and R is any of a group similar to R with the exception that it does not contain another CH OH(CHOH),,CH -radical.

2. The method of claim 1 wherein said hydroxy amine is a glucamine, having the general formula CHzOH(CHOH)4CHr-N wherein R and R represent the same substituents as in claim 1.

3. The method of claim 2 wherein said glucamine is diglucamine.

4. The method of claim 2 wherein said glucamine is monoglucamine.

5. The method of claim 2 wherein said glucamine is a glucamine crude obtained by hydrogenation of a mixture of glucose and ammonia in the presence of a hydrogenation catalyst at a pressure of at least 500 pounds per square inch gage.

6. The method of claim 1 wherein said hydroxy amine is a carboxyalkyl hydroxy amine derivative having the general formula /R CHz0H(CHOH) CHzN (CH2)=C where n is at least 2., x is a numeral of l to 3 and R is any of the group consisting of hydrogen, another 2 H( HOH)1;C g radical and another /0 -(orn).o

H radical.

atoms, an alpha carboxy group containing not more than 4 carbon atoms and a beta carboxy alkyl group contain-.- ing not more than 4 carbon atoms, exclusive of the carbon atom in the carboxy group, and R is any of a group similar to R with the exception that it does not contain another CH OH(COCH), CH -radical.

9. The composition of claim 8 wherein said etchin alkali is primarily caustic soda.

10. The composition of claim 8 wherein said hydroxy amine is a glucamine.

1 1. The compositionof claim 8 wherein said hydroxy amine is diglucamine.

12. The composition of claim 8 wherein said hydroxy amine is monoglucamine.

13. The composition of claim 8 wherein said hydroxy amine is a carboxy alkyl glucamine in which the alkyl group has not over 3 carbon atoms.

14. The composition of claim 13 wherein said carboxy alkyl glucamine is sodium methyl carboxy glucamine.

References Cited in the file of this patent UNITED STATES PATENTS 694,658 Meurant Mar. 4, 1902 2,650,875 Dvorkovitz Sept. 1, 1953 2,658,063 Tindall et al. Nov. 3, 1953 

1. THE METHOD OF ETCHING ALUMIUM COMPRISING TREATING SAID ALUMIUM AT AN ETCHING TEMPERATURE WITH AN AQUEOUS SOLUTION OF AN ETCHING ALKALI CONTAINING, IN AN AMOUNT SUFFICIENT TP PREVENT SCALE FORMATION, A HYDROXY AMINE HAVING THE GENERAL EMPIRICAL FORMULA 